The present invention relates to a varnish coater for a printed product, wherein the coater is arranged at the upstream side of a delivery unit of a rotary press or in an independent coating unit to apply varnish on a printed surface.
The surface of paper printed by a rotary printing press is not quickly dried and can be contaminated in the subsequent processing. In a sheet-fed rotary printing press, offsetting tends to be caused when printed sheets are attached. In order to solve these problems, conventionally, a dryer is arranged in a delivery path of the printed products, or a powder is sprayed on the printed paper surfaces. However, in this case, the dryer becomes large, and powder spraying results in surface roughening of the printed surface. Surface roughening tends to entail a loss of gloss and subsequent poor printing. Instead of these techniques, varnish is applied to the printed surface to prevent the surface from being contaminated and to give it gloss. Varnishing is performed in printed products such as covers of books, catalogs and pamphlets which require an aesthetic effect.
The varnish coater of this type is disposed between a printing unit and a delivery unit of a rotary press or in an independent coating unit. Furthermore, the varnish coater is used together with the dampening unit for the printing unit. The varnish coater generally has rollers in the same manner as that of a dampening apparatus for dampening a surface of a plate mounted on a plate cylinder of the printing unit. Varnish stored in a varnish pan is supplied to a surface of a blanket cylinder through the rollers. The varnish is transferred to a sheet passing between the blanket cylinder and an impression cylinder.
The varnish pan in the varnish coater has a bucket-like shape and is connected to an external varnish tank through piping. The temperature and concentration of varnish are adjusted to be uniform by a heater and stirring unit which are arranged in the varnish tank. The adjusted varnish is circulated by a pump. In order to perform uniform varnishing, the amount of varnish in the varnish pan must be kept constant. An overflow port is formed in the varnish pan to recover an excessive varnish portion to the varnish tank.
In the conventional varnish pan, the overflow port is formed at the upper portion of the varnish pan, and the pan roller is rotated. The upper layer of the varnish is stirred but the lower layer thereof will not be stirred. Therefore, the temperature of the lower layer of the varnish is decreased to increase the viscosity and concentration thereof. As a result, varnish having temperature and viscosity differences between the upper and lower layers is supplied to the varnishing portion, thus resulting in a nonuniform thickness of the varnish layer and hence degrading the product quality. In order to solve this problem, the varnish pan is periodically stirred. However, varnishing efficiency is degraded, and a great effect cannot be expected.